Heat Pump Alternate Refrigerants
The increased usage of hybrid and electric vehicles where waste heat availability is limited has spurred research and development of mobile heat pump systems. Many options exist for heat pump system architectures and refrigerants to be used. Currently R134a use is prevalent in vehicle air conditioning systems but offers poor heat pump performance at low ambient temperatures. Two refrigerants will be explored in this paper, R744 and R445A. Both of these refrigerants are getting attention in vehicle A/C systems because of their relatively low GWP but each offers benefits over R134a in heat pump systems as well. Both refrigerants operate at higher pressures which improves the performance at low ambient temperatures in part due to higher compressor inlet refrigerant densities. R134a (and R445A to a lesser extent) also suffer from the drawback of going into sub-atmospheric pressure operation at temperatures commonly seen in vehicles. Data will be shown for multiple system architectures comparing these refrigerants to R134a. Advantages and disadvantages of each refrigerant will be shown. System control and optimization is important to get the maximum performance from each refrigerant and system. Control exploration will be presented for each alternative refrigerant.